Rockwell Automation 6008-SV2R VMEbus remote I/O Scanner User Manual
Page 49
Chapter
Communicating with Remote I/O
4
4Ć12
Sending Multiple BlockĆTransfers to the Same Adapter
The scanner can send as many block-transfer requests as it needs to an
adapter (which corresponds to 1 physical rack), but it can only send one
block-transfer request to a rack per scan. To achieve the most efficient
block-transfers, arrange your intelligent I/O modules in multiple racks.
Another method to achieve faster block-transfers is to use the SCAN LIST
command so that a rack with several intelligent I/O modules is scanned
more often through multiple listings in the scan list.
The scanner keeps track of each block-transfer request by its unique tag
number. You assign the tag number when you configure the block-transfer
command. When a block-transfer command completes, the scanner returns
the tag number along with the data so your application can determine
which block-transfer completed.
In SV-compatible mode
Each scanner channel can queue as many as 42 block-transfer requests.
Each request has a block-transfer tag number that you assign in your
application program. When a specific block-transfer is complete, the
scanner sends the block-transfer tag number back to the VME master
processor, along with the data. This way, your application program will
know which block-transfer completed, since block-transfers do not
necessarily get completed in the same order they are requested.
In SV-superset mode
The scanner still processes a block-transfer request the same way as in
SV-compatible mode, but each scanner channel can queue only 1
block-transfer request. If you need multiple block-transfers to the same
adapter, use the continuous block-transfer operation. It achieves the same
result as sending several single block-transfer requests and it also reduces
programming overhead.
Before initializing a continuous block-transfer requeues to an I/O modules,
try a single block-transfer to the I/O module to verify the block-transfer
parameters. After verifying the single block-transfer, use those parameters
in a continuous block-transfer request.